This study will test the hypothesis that dysfunction of neuroendocrine regulatory structures (hypothalamus, pituitary gland, pineal gland) occurs in a subset of patients with closed-head injury. Because partial dysfunction of these structures presents with subtle clinical features, these features may be overlooked acutely but may contribute to non- specific symptoms, diminished quality of life during the recovery and rehabilitation of closed-head injury patients. We propose to investigate the frequency of neuroendocrine deficiencies in individuals recovering from closed head injuries by endocrine testing. This two year study will consist of two phases. In Phase I, recovering (at least 3 months post- injury) closed-head injury patients will be screened for the presence of neuroendocrine dysfunction with tests routinely used in clinical endocrinology. This will include assessment of adrenal, thyroid, and gonadal function, and prolactin and growth hormone secretion by the pituitary. In addition, melatonin secretion by the pineal galnd will be assessed via measurement of its principal urinary metabolite. One hundred subjects will be enrolled in Phase I. Any patient with an abnormal test result will undergo Phase II testing, in which dynamic tests of neuroendocrine function will be used. Results from this study could lead to standard neuroendocrine function testing of patients with closed-head injury in clinical practice. Subsequent hormone replacement would improve function and well-being in this group of patients.